Hundreds of companies across the United States are selling unapproved stem cell treatments directly to patients, raising concerns about safety and scams in a fast-growing industry, researchers said Thursday.

At least 351 companies across the United States are marketing unapproved stem cell procedures at 570 individual clinics, their report in the journal Cell Stem Cell found.

Researchers compiled the list by searching online, saying their results “should serve as a baseline for future studies of US businesses engaged in direct-to-consumer advertising of purported stem cell interventions,” the report said.

“In almost every state now, people can go locally to get stem cell ‘treatments,'” said co-author Paul Knoepfler of the University of California, Davis, and Shriners Hospital For Children.

“This is a marketplace that is dramatically expanding before our eyes,” said co-author Leigh Turner, a bioethicist at the University of Minnesota.

Such businesses have entered the marketplace routinely since 2009, he said.

“Does that mean that people are getting access to safe and efficacious interventions or is there basically unapproved human experimentation taking place?” he added.

“Brakes ought to exist in a marketplace like this, but where are the brakes? Where are the regulatory bodies? And how did this entire industry come into being in a country where stem cell-based interventions and the medical devices that produce them are supposed to be regulated by the FDA?”

The US Food and Drug Administration (FDA) has approved the use of stem cells for leukemia treatment — commonly known as bone marrow transplants — and some bone, skin and corneal diseases or injuries, according to the International Society for Stem Cell Research.

“Other stem cell treatments, while promising, are still at very early experimental stages,” the society’s website says.

The FDA will hold two meetings on the topic later this year, and “is concerned that the hope patients have for treatments not yet proven to be safe and effective may leave them vulnerable to unscrupulous providers of stem cell treatments that are illegal and potentially harmful,” the agency said in a statement.

It (Other OTC: ITGL – news) also urged consumers to “to learn all they can about the regulations covering any stem cell-based product they are considering” and has published a consumer update titled “FDA Warns About Stem Cell Claims.”

“Individuals considering stem cell therapy are urged to ask questions to ensure that the necessary FDA approval has been obtained,” the FDA said.